This invention relates to an intervertebral disc removing device. It allows for removal of the nucleus pulpous of an intervertebral disc, as well as the resurfacing of the vertebral end plate in preparation for nucleus replacement procedures or interbody fusion techniques.
Of all animals possessing a backbone, human beings are the only creatures who remain upright for significant periods of time. From an evolutionary standpoint, this erect posture has conferred a number of strategic benefits, not the least of which is freeing the upper limbs for purposes other than locomotion. From an anthropologic standpoint, it is also evident that this unique evolutionary adaptation is a relatively recent change, and as such has not benefited from natural selection as much as have backbones held in the horizontal attitude. As a result, the stresses acting upon the human backbone (or “vertebral column”) are unique in many senses, and result in a variety of problems or disease states that are peculiar to the human species.
The human vertebral column is essentially a tower of bones held upright by fibrous bands called ligaments and contractile elements called muscles. There are seven bones in the neck or cervical region, twelve in the chest or thoracic region, and five in the low back or lumbar region. There are also five bones in the pelvic or sacral region which are normally fused together and form the back part of the pelvis. This column of bones is critical for protecting the delicate spinal cord and nerves, and for providing structural support for the entire body.
Between the vertebral bones themselves exist soft tissue structures-discs-composed of fibrous tissue and cartilage which are compressible and act as shock absorbers for sudden downward forces on the upright column. More importantly, the discs allow the bones to move independently of each other, as well. Unfortunately, the repetitive forces which act on these intervertebral discs during repetitive day-to-day activities of bending, lifting and twisting cause them to breakdown or degenerate over time.
Presumably because of humans' upright posture, their intervertebral discs have a high propensity to degenerate. Overt trauma, or covert trauma occurring in the course of repetitive activities, disproportionately affect the more highly mobile areas of the spine.
Disruption of a disc's internal architecture leads to bulging, herniation or protrusion of pieces of the disc nucleus and eventual disc space collapse. Resulting mechanical and even chemical irritation of surrounding neural elements (spinal cord and nerves) cause pain, attended by varying degrees of disability. In addition, loss of disc space height relaxes tension on the longitudinal spine ligaments, thereby contributing to various types of spinal instability such as spinal curvature, ligamentous laxity or instability and spondylolithesis.
The time-honored method of addressing neural irritation and instability resulting from severe disc damage have largely focused on removal of the damaged disc and fusing the adjacent vertebral elements together. Removal of the disc relieves the mechanical and chemical irritation of neural elements, while osseous union (bone knitting) solves the problem of instability.
Once the disc has been removed, an implant may be installed in its place. Prior to implantation, in many situations, it is desirable or necessary to smooth or recontour the opposing vertebral surfaces. Proper preparation can be difficult and time-consuming.
U.S. Pat. No. 6,537,279 depicts a device for preparing an intervertebral endplate with an abrading element which is disc shaped.
In contrast, the abrading element of my device is linear and rotated like a propeller so it can be inserted through a much smaller opening in a disc and lends itself to minimally invasive techniques. Prior devices having disc-shaped cutters required an opening to be made in the disc annulus comparable in size to the diameter of the disc. The slender cutter of the present invention can be inserted through an opening much smaller than that required by a disc shaped cutter and hence is superior for minimally invasive techniques.
The present device also does not require screws to hold it in place in the disc space; moreover, the cutting surface can be expanded within the disc space to achieve greater force against the end plates. In contrast, the distance between the disc shaped cutters in the patent mentioned above is fixed by the gear drive mechanism used to drive both cutting discs simultaneously.
Because the abrading surfaces can be pressed apart while within the disc space, varying disc heights can be accommodated with a single device.
The device of the present invention has a flexible cutting blade which conforms itself to various contours in the endplate whereas prior cutting surfaces are fixed and their contours are predetermined, not variable. The propeller-like shape of the cutting or abrading surface is superior because it can be inserted through an opening the width of the propeller blade and still resurface a disc sized the length of the propeller blade.
One embodiment of the present invention has a dual shaft design which allows the abrading surfaces to be expanded away from each other to allow for use in discs of any height without any change of the drive means or the abrading elements. Additionally, the dual shaft design is superior as it allows the working cutting blades to be driven apart from each other to increase the force upon the blades while the blades are still in motion.